In swimming pools and spas, hydrochlorine (also called "liquid chlorine" or "chlorine") is a chemical necessary for disinfection of the water and to prevent the growth of algae. Dispensing is necessary to maintain the free form level of chlorine between 1.0 parts per million (ppm) to 1.5 ppm. At this level chlorine will effectively disinfect the pool water and prevent growth of algae. Also, the water at this chlorine level is considered safe for pool users. It is important that the chlorine level should not exceed 2.0 ppm as this might cause rash on the skin and/or irritation in eyes.
Usually, chlorine is dispensed into a pool daily. Correct amounts of chlorine are dispensed manually or by a chlorine dispensing device like a metering pump. The chlorine ppm level in the pool water is measured by a chlorine testing kit. If the chlorine level is too high, the dispensing of chlorine is decreased. If the chlorine level is to low, the dispensing of chlorine is increased. A chlorine dispensing device such as a metering pump runs on a manually set timer. Said chlorine dispensing device is activated each day when the pump is started for circulating the pool water. By manually setting the timer, the pump will dispense more or less chlorine.
Some systems dispense chlorine by using a chlorine sensor in the pool water. In such cases the metering pump will be started and stopped by the sensor's set point switches. However, a chlorine sensor is expensive and requires repeated calibration by a technician using a signal generator.
Many variables determine how much chlorine is needed. When water is cold (i.e. 5 to 10.degree. C.) very little chlorine is required. With increasing temperature, biological activity increases. Increased sunlight adds to the biological activity and will break down the chlorine effect more rapidly. Heavy pool use increases the chlorine demand. Also, evaporation of chlorine is increased at higher water temperatures. Thus, a proper ppm level is maintained longer at lower water temperatures than at higher water temperatures. Consequently, at lower temperatures you can keep the chlorine ppm level in the lower range of the recommended level for a satisfactory result. At higher water temperatures the chlorine ppm level should be maintained within the higher recommended range in order to achieve a good result. Many factors determine the curve for adding chlorine. For instance, an approximate 35,000 gallon pool requires an addition of 0.14 gallons at 10.degree. C., 0.2 gallons at 15.degree. C., 0.3 gallons at 20.degree. C., 0.44 gallons at 25.degree. C., and 0.7 gallons at 30.degree. C.
Currently, one must experiment with testing the chlorine ppm level and accordingly determine how much chlorine must be added. During this experimentation, it is easy to exceed the safe chlorine level and, possibly, to cause unhealthy conditions. High water temperatures in summer time will take less than twenty-four hours for the chlorine ppm level to return to zero. If the amount of chlorine is not added prudently and regularly, conditions are enhanced for algae growth. In such a case you incur additional cost for special chemicals to control algae. You have manual work for pool cleaning. The filter must be dismantled and cleaned plus the old filter powder must be replaced. Most of the time a pool will not be in operation during the algae-killing operation.
Most pool owners do not successfully manage the chlorine dispensing effectively. For this reason pool maintenance firms are employed for water disinfection and algae control.